Charge Order, Metallic Behavior, and Superconductivity in La_2-xBa_xCuO₄ with x=1/8

The ab-plane optical properties of a cleaved single crystal of La_2-xBa_xCuO₄ for x=1/8 (T_c≃2.4  K) have been measured over a wide frequency and temperature range. The low-frequency conductivity is Drude-like and shows a metallic response with decreasing temperature. However, below ≃60  K, corresponding to the onset of charge-stripe order, there is a rapid loss of spectral weight below about 40 meV. The behavior is quite different from that typically associated with the pseudogap in the normal state of the cuprates. Instead, the gapping of the normal-state single-particle excitations looks surprisingly similar to that observed in superconducting La_2-xSr_xCuO₄, including the presence of a residual Drude peak with reduced weight.